1. Field of the Invention
The present invention relates to the transmission of heated fluids. More specifically, this invention is directed to segmented conduits, which may be employed as tuyere feed lines for the delivery of preheated gas to the interior of a furnace and particularly to compensation joints for use in interconnecting the segments of such conduits. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in a temperature compensating joint in a tuyere feed line for a shaft furnace. In shaft furnaces, particularly in blast furnaces, preheated air is injected into the furnace through a plurality of injection nozzles located about the periphery of the furnace. These injection nozzles are connected to a common supply of preheated air by means of feed lines known as tuyere stocks. The heated gas supply will in part be in the form of a pipe, generally of circular cross-section, positioned coaxially of the furnace and spaced from the external furnace wall. The tuyere stocks typically comprise a number of serially connected tubular elements or segments which are internally lines with a refractory material.
In order to compensate for manufacturing and installation tolerances, and particularly to compensate for thermal expansion which occurs during the course of operation of the furnace, the adjacent segments of the tuyere stocks in the direction of gas flow are coupled together by means of swivel joints, bellows-type expansion compensators or compensators of the type employing Cardan joints.
For a further explanation of tuyere stocks, and particularly preheated air feed lines of the type employing Cardan compensators, reference may be had to U.S. Pat. 3,662,696 and 3,766,868. U.S. Pat. Nos. 3,662,696 and 3,766,868 which are assigned to the assignee of the present invention, are hereby incorporated herein by reference. The tuyere stocks of the referenced patents offer the advantage of permitting compensation for differential deformations during use and manufacturing inaccuracies between tubular segments of a tuyere stock to be achieved through the use of Cardan joints in conjunction with bellows-type compensators having a very small number of corrugations.
To summarize, the state of the art, it is known to provide articulated temperature compensation joints between segments of a tuyere stock which is employed to deliver preheated air from a common supply pipe to an injection nozzle in the wall of a shaft furnace. U.S. Pat. Nos. 3,662,696 and 3,766,868 show and describe compensation joints which have proven to be highly successful. These compensators employ Cardan joints and bellow-type elements; the bellows elements being employed to provide hermetic sealing about the articulation surfaces of the joint assembly. The bellows elements, which are directly exposed to the heated gases, are the components of the tuyere stock compensation joints most susceptible to deterioration as a result of the extremely high operating environment temperature. Potential failure of the bellows-type elements presents a serious safety hazard and compensation joint repair or replacement, either when a bellows failure occurs or as part of a required preventative maintenance schedule, has a deleterious effect on the efficiency of operation of the furnace. Thus, it has for some time been desired to limit the temperature of the bellows-type elements of tuyere stock compensator joints. Also, considering the compensator joints of the referenced U.S. patents, the bellows-type elements are fabricated from special high temperature steels. It would be desirable in the interest of minimizing joint manufacturing expense through the use of less costly materials, to use standard materials but this result can be realized only through preventing over-temperature of the bellows-type elements.